1. Field of the Invention
The present invention relates to a drive power transmission apparatus in a four-wheel-drive vehicle, in which a drive power distribution apparatus is assembled within a sub-axle type transmission apparatus.
2. Related Art
Language in the Japanese unexamined patent application publication 8-21503 describes a sub-shaft toroidal type stepless transmission, denoted by reference numeral 1001 in FIG. 10 of the accompanying drawings.
The toroidal type stepless transmission 1001 is used in a dual-shaft drive vehicle, and has a torque converter 1003, a forward/reverse switching mechanism 1005, stepless transmission mechanisms 1007 and 1009, and an output unit 1011.
The drive power of a motor is transmitted from the torque converter 1003 to the forward/reverse switching mechanism 1005. The forward/reverse switching mechanism 1005 is formed by a planetary gear and multivane clutch or the like, and performs switching in accordance with the rotational direction of the transmitted drive power, being either forward or reverse, which is then transmitted to the stepless transmission mechanisms 1007 and 1009.
The stepless transmission mechanism 1007 has a pair of input disc 1013 and output disc 1015, a friction roller 1017, an input shaft 1019, and an output shaft 1021, and the stepless transmission mechanism 1009 has a pair of input disc 1023 and output disc 1025, a friction roller 1027, and also, in common with the stepless transmission mechanism 1007, has the input shaft 1019 and the output shaft 1021
The input shaft 1019 is linked to the forward/reverse switching mechanism 1005, and the output shaft 1021 is disposed at the outer periphery of the input shaft 1019.
The input disc 1013, the output disc 1015, the input disc 1023, and the output disc 1025 are each disposed so that the profiles of the frictional surfaces thereof form a circle and are in mutual opposition, the input discs 1013 and 1023 are fixed to the input shaft 1019, and the output discs 1015 and 1025 are fixed to the output shaft 1021.
The friction rollers 1017 and 1027 are pressed up against the frictional surfaces of the input disc 1013 and output disc 1015, and the frictional surfaces of the input disc 1023 and the output disc 1025, respectively, drive power transmitted from the forward/reverse switching mechanism 1005 to the input shaft 1019 being transmitted via the friction rollers 1017 and 1027 by frictional forces developed at their frictional surfaces to the output discs 1015 and 1025 and causing the output shaft 1021 to rotate.
When the above occurs, if the friction rollers 1017 and 1027 are rocked so as to change the angle of inclination, there is a change in the radius of contact with each disc, so that, for example, if an inclination is imparted in a direction so that the radius of contact of the friction rollers 1017 and 1027 with the input discs 1013 and 1023 is increased and the radius of contact with the output discs 1015 and 1025 decreases, then the speed of the output shaft 1021 increases, and if the imparted inclination is in the reverse direction, then the speed of the output shaft 1021 is reduced.
The output unit 1011 has gear sets 1029 and 1031, a sub-shaft 1033, an idler (not shown), an output shaft 1035, and the like.
The gear set 1029 interconnects the output shaft 1021 and the sub-shaft 1033. The gear set 1031 is formed by a gear 1037 on the sub-shaft 1033, a gear 1039 on the output shaft 1035, and the idler that interconnects the gears 1037 and 1039, and serves for interconnection between the sub-shaft 1033 and the output shaft 1035.
The output shaft 1035 is disposed coaxially with respect to the torque converter 1003, the forward/reverse switching mechanism, and the stepless transmission mechanisms 1007 and 1009, and the sub-shaft 1033 is parallel to these elements.
Drive power output from the stepless transmission mechanisms 1007 and 1009 to the output shaft 1021 is sent to wheels from the gear set 1029, via the sub-shaft 1033, the gear set 1031, and the output shaft 1035.
As described above, the stepless toroidal transmission 1001 is used in a two-wheel-drive vehicle. For use in a four-wheel-drive vehicle, to reduce the size and weight of the vehicle and enable the achievement of a low-cost four-wheel-drive vehicle, a power distribution unit is combined with an existing transmission (as a speed change gear) for a two-wheel-drive vehicle.
In the case of the stepless toroidal transmission 1001, however, in which the output unit of a sub-shaft type transmission is made up of a sub-shaft 1033, a gear set 1031, and an output shaft 1035 and the like, if an input of the power distribution unit is linked to the output shaft 1035, both the axial length of the combined transmission and power distribution unit increases, and the combined weight increases.
With an increased axial length, it is necessary to make a change in the propeller shaft and casing (transmission case and power distribution unit case), thereby causing a great increase in cost.
Existing transmissions have idle gears and torque-adjusting gear sets and the like for the purpose of rotational direction adjustment. For example, there is a case in which a gear set corresponding to the gear set 1031 of the stepless toroidal transmission 1001 has gears 1037 and 1039 on the sub-shaft 1033 and the output shaft 1035, and an idle gear linked thereto, and a case in which this idle gear and the gear 1039 on the output shaft 1035 serve as a gear set for torque adjustment.
If the power distribution unit is assembled together with a transmission having such an idle gear or torque adjustment gear, because the idle gear or torque adjustment gear gives restriction to the mounting (connection) of the power distribution unit, in addition to an overall increase in size of the combined transmission and power distribution unit, it becomes difficult to achieve a reduction in cost.
Accordingly, it is an object of the present invention to provide a lightweight, compact, and low-cost power transmission apparatus, by combining various sub-shaft type transmission apparatuses with a power distribution apparatus.
More specifically, a first aspect of the present invention provides a power transmission apparatus comprising a transmission apparatus for outputting drive power of a motor from an input shaft, via a transmission mechanism disposed coaxially therewith, to a sub-shaft disposed in parallel thereto; and a power distribution apparatus disposed in parallel to the sub-shaft, for transmitting rotation of an input end member linked to an end of the sub-shaft, via respective output shafts, to a front-wheel end and a rear-wheel end, wherein at least the sub-shaft and the input end member are disposed in an axially overlapping relationship.
It is noted that in the present invention The phrase xe2x80x9cthe sub-shaft and the input end member are disposed in an axially overlapping relationshipxe2x80x9d means that, when the sub-shaft and the input end member are radially projected, their projections have mutually overlapping parts.
The xe2x80x9cmotorxe2x80x9d as used above will be understood herein as meaning an internal combustion engine, or a motor converting electrical energy to rotative power.
In this manner, in the present invention, by linking an input end member to a sub-shaft of a sub-shaft type transmission apparatus, an existing power transmission apparatus for two-wheel driven vehicle is available to implement a power transmission for four-wheel driven vehicle.
Because at least the input end member of the power distribution apparatus has an axially overlapping relationship with the sub-shaft type transmission apparatus, it is unnecessary to change the axial dimension of the sub-shaft, or extremely suppressed, in addition to that the power transmission apparatus (power distribution apparatus and transmission apparatus) can be reduced by the overlapping dimension in the axial direction, allowing for the size to be compact, the weight to be prevented from being increased, and the mountability to be improved.
The interconnection between the sub-shaft disposed upstream in a drive power transmission route of the power distribution apparatus and the input end member of the power distribution apparatus does not involve the gear set 1031 and the output shaft 1035 in such a sub-shaft type transmission the conventional stepless toroidal transmission 1001, nor an idle gear or torque control gear.
Therefore, from the existing sub-shaft type transmission apparatus, simple power transmission members therein as such intermediate members as gear set 1031, output shaft 1035, idle gear, and torque control gear, are eliminated, having a reduced number of components, allowing for compact size, light weight, and low cost.
Changes or modifications more than removing those intermediate members, for example, such a change or modification as a change in size of the sub-shaft or a modification of the casing, are not necessitated nor possibly suppressed, so that the power transmission apparatus for four-wheel driven vehicle can be achieved with an extremely low cost, with an existing layout maintained.
The casing can be made compact in size in accordance with the compactness and lightweight of the power transmission apparatus, having a wall thinned and lightweighted with an improved rigidity.
According to a second aspect of the present invention, in a power transmission apparatus according to the first aspect, the power distribution apparatus and the sub-shaft are disposed in an axially overlapping relationship. There can be achieved like functions and effects to the first aspect.
Further, an entirety of the power distribution apparatus axially overlaps the sub-shaft, with commensurate compactness and enhancement of vehicle mountability.
According to a third aspect of the present invention, in a power transmission apparatus according to the first or second aspect, the sub-shaft and the input end member are linked via a speed changing mechanism, and the speed changing mechanism comprises a plurality of stages of gear sets operative for a speed change by an operation mechanism. There can be achieved like functions and effects to the first or second aspect.
Because the speed changing mechanism can be disposed in such a space as for the gear 1037 of the conventional gear set 1031, a speed changing function is available, making effective use of an existing space.
Because the speed changing mechanism can be formed simply by those members (gears) disposed on the input side member and the sub-shaft, without using members on other shafts, for example, idle gears, it is possible to have a low-cost arrangement with a reduced number of components, avoiding increase in weight or enlargement in radial direction.
In this manner, an existing space is available for installation of the speed changing mechanism, without needing provision of a new installation space, without the need of changing a conventional layout, thus allowing for implementation at a low cost.
Because the speed changing mechanism and the sub-shaft are disposed mutually coaxial, allowing disposition of, for example, a differential mechanism or coupling, it is possible to achieve a function therefrom, for example, a differential function or intermittent torque connecitng funtion, with a conventional layout maintained.
It is noted that the speed changing mechanism means a shift mechanism, such as a High-Low shift mechanism (hereafter called xe2x80x9cHi-Lo shift mechanismxe2x80x9d), and a direction switch mechanism that switches between forward and reverse directions. The shift mechanism is not limited to a two-stage shift, and may be a plural-stage shift.
The Hi-Lo shift mechanism may preferably be used for a sub-shift gear set in a four-wheel driven vehicle, such as an off-road vehicle.
According to a fourth aspect of the present invention, in a power transmission apparatus according to the third aspect, the speed changing mechanism has operation means disposed coaxially with the sub-shaft. There can be achieved like functions and effects to the third aspect.
Because the speed changing mechanism and operations therefor are disposed coaxially with the sub-shaft, it is possible to arrange the operation means in a space of the gear 1037 that constitutes the gearset 1031 of the stepless toroidal transmission 1001, for example.
In this manner, an existing installation space is available, avoiding a region in which components such as the speed changing mechanism are concentrated in the casing, without needing provision of a new installation space, without the need of changing a conventional layout, thus allowing for implementation at a low cost.
According to a fifth aspect of the present invention, in a power transmission apparatus according to any one of the first to fourth aspects, the power distribution apparatus has a differential mechanism for allowing differential rotation between the respective output shafts. There can be achieved like functions and effects to the first to fourth aspects.
In this configuration, drive power of the motor is transmitted by the differential mechanism to the the front and rear wheels, allowing for a full-time four-wheel driven vehicle to be implemented very compact.
In the case of a differential mechanism adjustable of a torque distribution ratio between front wheel end and rear wheel end (for example, in a gear type differential mechanism, by changing the front wheel end gear ratio and the rear wheel end gear ratio), the drive power distribution ratio between front and rear wheels can be set as desirable.
According to a sixth aspect of the present invention, in a power transmission apparatus according to the fifth aspect, a difference limiting mechanism for limiting the differential rotation of the differential mechanism is disposed coaxially with the power distribution apparatus. There can be achieved like functions and effects to the fifth aspect.
Because the difference limiting mechanism is disposed coaxially with the power distribution apparatus, interconnection between the different limiting mechanism and the differential mechanism is simplified in structure, allowing for the power transmission apparatus to be commensurately compact.
When the difference limiting mechanism is operated, or when differential rotation is locked by the difference limiting mechanism, wheels are prevented from skidding, thereby improving the ability of the vehicle to negotiate poor road surfaces, starting performance, acceleration performance, body stability, and direction stability.
By stopping the operation of the difference limiting mechanism, or by canceling the difference rocking, such vehicular characteristics as head direction changeability and turnability, as well as fuel consumption of the motor, can be improved.
By adjusting a difference limiting force of the diffrence limiting mechanism in accordance with variations such as of road surface condition, steering condition, and acceleration condition, it is possible to select an optimum condition between the effect of improvements, when diffrence is limited, such as in the ability of the vehicle to negotiate poor road surfaces, starting performance, acceleration performance, body stability, and direction stability, and the effect of improvements, when the difference is allowd, such as in head direction changeability and turnability, as well as in fuel consumption.
According to the seventh aspect of the present invention, in a power transmission apparatus according to the sixth aspect, the difference limiting mechanism comprises a clutch mechanism for locking the differential rotation. There can be achieved like functions and effects to the sixth aspect.
By a difference locking function of the clutch mechanism, even over a poor road surface or a low-xcexc road surface, the wheels are prevented from skidding, thereby improving the ability of the vehicle to negotiate poor road surfaces, starting performance, acceleration performance, body stability, and direction stability, and by cancellation of the difference locking, there allowed improvements of such vehicular characteristics as head direction changeability and turnability, as well as fuel consumption of the motor.
According to an eighth aspect of the present invention, in a power transmission apparatus according to the sixth or seventh aspect, the difference limiting mechanism is disposed serially to the power distribution apparatus. There can be achieved like functions and effects to the sixth or seventh aspect.
In accordance with a splitting structure and split location of a casing accommodating the power transmission apparatus, and a spacing between the casing and the difference limiting mechanism, as well as with whether interferencces are present or not between the difference limiting mechanism and vehicle body end peripheral members, the difference limiting mechanism is allowed to have the location for disposition selected for the assembly, with a facilitated implementation.
Operation means for the difference limiting mechanism may for example be a fluid pressure actuator, such as a hydraulic actuator, or an actuator using a magnet or an electric motor. Anyhow, in this arrangement in which the location for disposition of the difference limiting mechanism is selective in accordance with peripheral members and their layout, it is possible for example to serially dispose the difference limiting mechanism outside the differential mechanism, and in this case, pressure lines for the fluid pressure actuator and lead wires for the magnet or electric motor are prevented from interfering with the differential mechanism, with facilitated piping and wiring installation, with advantages in layout.
According to a ninth aspect of the present invention, in a power transmission apparatus according to any one of the first to fourth aspects, the power distribution apparatus comprises a coupling adapted at one output shaft end for normally transmitting drive power and at another output end for intermittently transmitting drive power as necessary. There can be achieved like functions and effects to the first to fourth aspects.
In this configuration, which employs a coupling smaller in size and lighter in weight than the differential mechanism, it is possible to improve the vehcile mountability, avoiding enlargement in size and increase in weight, when implementing a power transmission apparatus for four-wheel driven vehicle according to the present invention.
By using as the coupling a coupling of a torque control type in which an engagement force of a friction clutch is adjustable with a fluid pressure actuator such as a hydrauloic actuator or an actuator such as a magnet or electric motor, it is allowed to adjust drive power to be transmitted to wheels at one output end in dependance such as on a skidding condition (road surface condition) of wheels at another output end, running condition of the vehice, and steering condition, thereby improving the ability of the vehicle to negotiate poor road surfaces, starting performance, acceleration performance, and the like to a sufficient degree.
If the coupling to be used is a rotation difference sensitive type that transmits drive power in accordance with the rotation difference by the shearing resistance of a viscous fluid, as the skidding speed of a wheel increases at one end, the larger drive power is transmitted to a gripping wheel at the other end, allowing for the vehicle to have a greatly improved ability to negotiate poor road surfaces.
The rotation difference sensitive type coupling may be such one that employs the resistance at a delivery orifice of a hydraulic pump to produce a difference limiting force, or such one that combines a friction clutch with the shearing resistance or the pressure due to shearing resistance, as well as the orifice resistance or the delivery pressure.
The rotation difference sensitive type coupling, which does not use an actuator unlike the torque control type coupling, allows the power transmission apparatus to be the smaller in size and lighter in weight.
If the coupling to be used is an on-off switching type which intermittently transmits torque to a wheel at the output end, it is possible for an on-demand to make selection between a four-wheel driven state and a two-wheel driven state.
The switching type coupling is small in size and light in weight like the rotation difference sensitive coupling, so that the power transmission apparatus can be compact and lightweight.
According to a tenth aspect of the present invention, in a power transmission apparatus according to any one of the first to ninth aspects, the respective output shafts at the front wheel end and the rear wheel end of the power distribution apparatus are linked to power takeout shafts disposed in parallel thereto respectively, and drive power is transmitted via the power takeout shafts to the front wheel end and the rear wheel end. There can be achieved like functions and effects to the first to ninth aspects.
In this configuration, which has power takeout shafts linked to the respective connection shafts at a front wheel end and a rear wheel end of the power distribution apparatus, respective torque takeout parts at the front wheel end and the rear wheel end can be provided in arbitrary axial positions, with a prevention of interferences between the torque takeout parts and the casing and peripheral members, with a facilitated implementation of the power transmission apparatus.
For such reasons, not simply the shape and size of the casing, but also the peripheral members as well as the layout at the vehicle body end can have an enhanced freedom in design, allowing for a flexible coping with various environmental conditions, with possible applications to a wide range of different vehicle types.
According to an eleventh aspect of the present invention, in a power transmission apparatus according to the tenth aspect, an interconnection between a front wheel end output shaft and the power takeout shaft thereof and an interconnection between a rear wheel end output shaft and the power takeout shaft thereof are made at locations radially different with respect to a rotation axis of the power distribution apparatus. There can be achieved like functions and effects to the tenth aspects.
In this configuration, in which the power distribution apparatus has a pair of torque takeout parts disposed at different locations in the radial direction, the torque takeout parts as well as their extensions are free from mutual interferences that otherwise, for example in the case they are disposed in opposition in the radial direction, might have been experienced.
The torque takeout parts may be radially disposed at a predetermined angle relative to each other in accordance with the condition of lubrication of their bearings for support or linking gear parts in the casing.
It therefore is unnecessary to provide the torque takeout parts with extensions or the like for avoiding mutual interference, and it is avoidable to make the power transmission apparatus axially long, thus allowing for the apparatus to be kept compact and high of vehicle mountability.
The torque takeout parts can be provided both on one side or either on both sides of the axial direction of the power distribution mechanism, in addition to that axial extensions provided on the torque takeout parts are free from mutual interference as described, and can have connections to the front and rear wheels at arbitrary locations.
In this manner, the configuration according to the eleventh aspect is greatly effective to avoid intereference with peripheral members.
For such reasons, not simply the shape and size of the casing, but also the peripheral members as well as the layout at the vehicle body end can have an enhanced freedom in design, allowing for a flexible coping with various environmental conditions, with possible applications to a wide range of different vehicle types.
According to a twelfth aspect of the present invention, in a power transmission apparatus according to the tenth or eleventh aspect, the front wheel end output shaft and the rear wheel end output shaft of the power distribution apparatus are disposed axially at both sides of the power distribution apparatus, and linked to the power takeout shafts respectively. There can be achieved like functions and effects to the tenth or eleventh aspects.
In this configuration in which output shafts of the power distribution apparatus are distributed either to both sides of the axial direction, the power distribution apparatus is disposed in an axially central region, with a facilitated axial balancing to reduce vibrations and noises accompanying the rotation, allowing for the durability of bearings to be improved.
In a layout in which the power distribution apparatus is disposed intermediate between the front and rear wheels, such drive power transmission routes up to the differential apparatus (such as propeller shafts) that are provided between the power takeout parts as well as between the front wheels or rear wheels are short, and the torsional vibration is small, thus allowing an improved durability.
According to a thirteenth aspect of the present invention, in a power transmission apparatus according to the twelfth aspect, the front wheel end output shaft of the power distribution apparatus is disposed axially at the front wheel end and the rear wheel end output shaft of the power distribution apparatus is disposed axially at the rear wheel end, to be linked to the power takeout shafts respectively. There can be achieved like functions and effects to the twelfth aspect.
In this configuration in which the output shaft at the front-wheel end is disposed on the front-wheel side of the axial direction of the power distribution apparatus and the output shaft at the rear-wheel end is disposed on the rear-wheel side of the axial direction of the power distribution apparatus, radial dimensions about the power distribution apparatus can be small, and axial dimensions of the power takeout shafts can be reduced.
According to a fourteenth aspect of the present invention, in a power transmission apparatus according to the tenth or eleventh aspect, the front wheel end output shaft and the rear wheel end output shaft of the power distribution apparatus are disposed axially at one end of the power distribution apparatus, to be linked to the power takeout shafts respectively. There can be achieved like functions and effects to the tenth or eleventh aspects.
In this configuration in which the respective output shafts of the power distribution apparatus are disposed both on one side of the axial direction of the power distribution apparatus, their supporting parts can be collected at one point, and interconnections between the output shafts and power takeout parts can be mutually radially provided, with commensurate compactness in the axial direction of the power distribution apparatus.
According to a fifteenth aspect of the present invention, in a power transmission apparatus according to any one of the tenth to fourteenth aspects, the speed changing mechanism of the transmission apparatus comprises a stepless toroidal transmission configured with an input disc linked to the input shaft an output disc linked to a transmission member at an output end, and a friction roller contacting the discs, for rotation of the input disc to be changed in speed by a rocking operation of the friction roller and transmitted to the output disc, and the power distribution apparatus is disposed for a linking in which directions of rotation of the power takeout shafts of the front wheel end output shaft and the rear wheel end output shaft and the sub-shaft are identical. There can be achieved like functions and effects to the tenth to fourteenth aspects.
The stepless toroidal transmission may for example be one of a double cavity type, which has two output discs disposed back-to-back and two input discs disposed at both axial ends thereof, and a single cavity type, in which input and output discs are arranged one by one, although in either case there are needed elements, such as an idler shaft, to make the identical directions of rotation of a sub-shaft and a power takeout shaft for taking out drive power from the output disc.
To this point, the present invention, in which a sub-shaft of an existing sub-shaft type transmission apparatus and a power distribution apparatus are combined to constitute a power transmission apparatus for four-wheel driven vehicle to be compact in size and light in weight is very suitable for combination with such a stepless toroidal transmission as described.
In addition to the compact and lightweight configuration, the combination with a stepless toroidal transmission can enjoy many advantages of the stepless toroidal transmission, such that it is free from interruption of torque during speed change, and capable of smooth running free of speed change shock, and can have a linear response to accelerating operations, and perform a travel under a condition highest of motor efficiency, allowing for greatly improved fuel consumption.
Because the power distribution apparatus can be provided with existing component configuration and arrangement by employing such a linking that the power takeout shafts of front-wheel end output shaft and rear-wheel end output shaft have identical directions of rotation, the power transmission apparatus can be configured compact with an existing layout maintained.